Methylisothiazolinone
AKA “2-Methyl-4-isothiazolin-3-one, 2-Methyl-3(2H)-isothiazolone, 2-Methyl-4-isothiazoline-3-one, N-methylisothiazolone, 3(2H)-Isothiazolone, 2-methyl-3-isothiazolone, n-methylisothiazolin-3-one, Neolone 950”
Synthetic
Ingredient Facts
Methylisothiazolinone
AKA: 2-Methyl-4-isothiazolin-3-one, 2-Methyl-3(2H)-isothiazolone, 2-Methyl-4-isothiazoline-3-one, N-methylisothiazolone, 3(2H)-Isothiazolone, 2-methyl-3-isothiazolone, N-methylisothiazolin-3-one, Neolone 950
Synthetic · Antimicrobial · EWG: 4
Synthetic
Preservative
Medicated Active
Synthetic
Clean
A synthetic preservative that keeps products fresh and prevents bacterial growth, used in rinse-off formulas like cleansers and shampoos.
Solubility Solubility in: acetonitrile 78.6; methanol 79.1; hexane 2.371; xylenol 15.65 (g/100 mL)
Formula
C4H5NOS
Mol. Weight
115.16
CAS #
2682-20-4
Form
Liquid
State
NKRA; Liquid
See origin →
Functions
Preservative
Keeps your product from growing bacteria, mold, or yeast. Without these, that jar of cream becomes a petri dish in about a week.
Antimicrobial
Keeps your product from growing bacteria, mold, or yeast. Without these, that jar of cream becomes a petri dish in about a week.
Preserves Formula
Prevents microbial growth
Traditional Use
Synthesized in the 1970s as a preservative and biocide for cosmetics, personal care, and industrial products. Designed to be a more stable alternative to earlier isothiazolinone preservatives.
Skin Types
●all-skin-types
Best For
General
Melanin-Rich Skin
Suitable
Pregnancy & Breastfeeding Safe
Caution
Allergen Warning
⚠️ MI/MCI Preservative
EWG
4
CIR
Safe w/Qualifications
Pregnancy
Caution
Restricted By
CIR Safety Findings
Not a Sensitizer
medical-approval
all-shades-safe
Concentration Guide
0.01%
0%0%
Reg. Limit
EU regulatory limit: 0.01%. Source: EU Cosmetics Regulation (EC) 1223/2009, Annex V (Preservatives), Entry 57.
Regulatory Agencies
Contact allergy caused by methylisothiazolinone: the Belg...
Olivier Aerts, An Goossens, Françoise Giordano-Labadie
European journal of dermatology : EJD, 2015
Methylisothiazolinone.
Mari Paz Castanedo-Tardana, Kathryn A Zug
Dermatitis : contact, atopic, occupational, drug, 2013
Amended Safety Assessment of Methylisothiazolinone as Used in Cosmetics
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Ammended Safety Assessment of Methylisothiazolinone and Methylchloroisothiazolinone as Used in Cosmetics
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Final Report of the Safety Assessment of Methylisothiazolinone
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Final Report on the Safety Assessment of Methylisothiazolinone and Methylchloroisothiazolinone
Cosmetic Ingredient Review (CIR) Expert Panel
International Journal of Toxicology
Methylisothiazolinone
European Commission
EU Cosmetic Ingredient Database (CosIng)
Methylisothiazolinone
Environmental Working Group (EWG)
EWG Skin Deep Cosmetics Database
Methylisothiazolinone (MI)
Health Canada
Health Canada Cosmetic Ingredient Hotlist
Methylisothiazolinone / Methylchloroisothiazolinone, in combination
Health Canada
Health Canada Cosmetic Ingredient Hotlist
Methylchloroisothiazolinone and/or methylisothiazolinone in cosmetic products-A market survey.
Sukakul T, Kanchanapenkul D, Bunyavaree M, Limphoka P, Kumpangsin T et al.
Contact dermatitis, 2019
The epidemic of methylisothiazolinone contact allergy in ...
W Uter, K Aalto-Korte, T Agner, K E Andersen, A J Bircher, R Brans + 13 more
Journal of the European Academy of Dermatology and Venereology : JEADV, 2020
Verified Feb 2026
Data: PubChem · CosIng · EWG · CIR